4.3.11.6 Tagged Seismic Data

The imported volumes may contain any data. However several types can be specified during import and/or after:

• Depth poststack volumes/lines loaded in time surveys. A check box must be toggled on during SEG-Y or simple file import.
• Time poststack volumes/lines loaded in depth surveys. A check box must be toggled on during SEG-Y or simple file import.
• Velocity/anisotropy volumes must be tagged with respect to their type, when imported from an external file. The available types are:
• Vint: Interval velocity
• Vrms: RMS velocities (time domain only). A provided surface may provide elevation statics in meters. For time surveys a statics velocity must be provided in m/s, either from a velocity grid or using a constant velocity.
• Vavg: Defined as the ratio between the depth and the travel time: Vavg(TWT)=2*Z/TWT=Z/OWT.
• Delta: Thomsen anisotropy parameter of the same name.
• Epsilon: Thomsen anisotropy parameter of the same name.
• Eta: Effective anisotropy parameter, combine from delta and epsilon. This tag can also be used to grid another quantity (the software does not actually check that eta values are input).

The assignment of velocity types (and properties) to a volume is called velocity edition. This window can be opened in most windows wherever velocity volumes are used (an exception is the attribute set window):

• Volume gridding
• Time-to-depth scenes
• Time-to-depth conversions
• Velocity conversions

Application of velocity corrections on prestack gathers

The velocity volumes may be scanned to get the Vavg range at their first and last sample. This allows the software to deduct and propose appropriate time/depth ranges during conversions (on-the-fly and batch).